Modelling the spatio-temporal interplay between North Sea saithe (Pollachius virens) and multiple fleet segments for management evaluation

Abstract

-There is growing interest in bio-economic models as tools for understanding pathways of fishery behaviour, in order to assess the impact on natural resources. Based on 'FishRent', a modelling approach is presented that integrates economics of the fleet, the impact of fishing on stock development and their spatio-temporal interplay. The simulation of species seasonal movements in combination with both observed values and stochastic recruitment allowed analysing the economic response of fleet segments to changes in stock distribution and development. Optimisation of net profits determines the effort adjustment and spatial allocation of fleet segments, which in turn affects the level of catch rates. Effort tended to concentrate where fish abundance was high, but also where fishing costs were low. In simulations with the current management plan spawning stock of North Sea saithe (Pollachius virens) declined below its precautionary reference point. In response fishing far from home ports became expensive and 40% of the initial effort was shifted to areas closer to home ports, but as areas of high fish concentrations were located by the modelled fleet segments catch rates remained high. Changes in seasonal/annual stock distribution, the stock decline and costs influenced the change in fishing effort distributions leading to overestimated catch per unit of effort values that masked the decline of stock abundance.

Hump‐shaped relationship between aggregation tendency and body size within fish populations

“…feeding and wintering migration, might have intertwined with the effect of spawning behaviors. For example, haddock, whiting and saithe spawn in winter/spring, while they migrate to the feeding ground or post‐spawning ground in summer (Daan et al 1990, Tobin et al 2010, Simons et al 2014).…”

Reconciling complex system models and fisheries advice: Practical examples and leads

“…The call explicitly requested models that include technical interactions, allow the split into fleet segments or gears, implement changes in selectivity (as a proxy to simulate area/time closures) and split catches into two categories, below and above Minimum Conservation Reference Size (STECF 2015). To answer this call, a large diversity of models were used (ISIS-Fish, Ecopath with Ecosim (EwE), FLBEIA, Fcube, IAM (Macher et al 2008), Simfish (Bartelings et al 2015) and Fishrent (Simons et al 2014)).…”